The present invention relates to orthopaedic devices, and, in particular, to devices providing improved alignment and coupling between the vertebrae of the spine and a longitudinally extending surgical rod. This invention is related to application Ser. No. 669,651, now U.S. Pat. No. 5,122,131 entitled "Orthopaedic Device for Mechanical Coupling to a Surgical Rod" and filed concurrently herewith.
The use of longitudinally extending surgical rods in the treatment of the diseases of the spine, such as scoliosis, kyphosis, and instability, is well-kmown in the medical arts. Such rods achieve rigid spinal fixation when mechanically coupled to bone anchor attachments, such as hooks or screws. These surgical rods are used, generally, in pairs placed on the posterior surface of the left and right sides of the lamina of the human spine.
One widely used anchor attachment is the conventional orthopaedic hook having a block-shaped head portion, with a central, cylindrical bore therethrough, and a hook portion. The bore of the conventional orthopaedic hook is adapted to receive the surgical rod, and the head is slidably positioned over the surface of the surgical rod to the selected vertebra for attachment. The hook may have a variety of different shapes, lengths and openings to accommodate the specific vertebra to which it is to be anchored. With the hook portion properly anchored, the conventional orthopaedic hook is locked to the surgical rod either by ratchet or by one or more setscrews located within the block-shaped head.
Another anchor attachment is a special orthopaedic screw having a block-shaped head with cylindrical bore therethrough. The screw, when its threaded end is attached to the selected anatomical site, is adapted for receiving and passing the elongated surgical rod through its cylindrical bore. Since the shank and threaded end of the screw extends perpendicularly with respect to the axis of the bore, once the screw has been anchored the position of the head, with its cylindrical bore, is fixed with respect to the spine of the patient.
If the nature of the disease of the spine should require the attachment of a number of orthopaedic screws at spaced-apart anatomical sites, it will be appreciated that manual insertion of an elongated surgical rod through the bores of the several spaced-apart orthopaedic screws is surgically difficult. The alignment of the axis of the bore in the head of each screw must, of necessity, bear some relationship to a common axis related to the axis of the surgical rod, which rod must be inserted through the several bores. Since the nature of the surgical operation places the surgical rod under stress, as by resisting deforming forces of the spine, it will be appreciated that proper positioning of the heads and alignment of the bores of the several anchor attachment members is of paramount concern.
With the conventional orthopaedic hook, it is frequently found that when the hook is inserted over, or under, the selected vertebra to which it is to be anchored, the axis of the bore through the head of the hook does not fall into the axial alignment desired. In such case, the hook must either be altered or replaced with another of different length, shape or opening.
Recognizing that the surgical rods, with their anchor attachments, are installed during open-back surgery, while the patient is under anesthesia, it is important for the orthopaedic surgeon to have available for immediate use anchor attachments that are easily positioned and aligned between the vertebrae and the surgical rods to which they are to be secured.
The present invention introduces an orthopaedic device having angularly adjustable anchor attachment members for mechanical intercoupling between selected vertebrae of the spine and a surgical rod. The device includes a block-shaped member having a central cylindrical bore within which the surgical rod is to be positioned and secured. The block-shaped member includes a recessed, hollow socket extending part way into the block-shaped member between the central bore and the rear surface thereof. An aperture extends from the bottom of the recessed, hollow socket out through the rear surface of the block-shaped member. The recessed, hollow socket serves to retain and support the head of an angularly adjustable and removable anchor attachment member. One angularly adjustable and removable attachment is the novel orthopaedic hook member of the invention, which hook member includes a short, rod-shaped cylindrical head portion, a shank portion, and a hook portion. The shank and hook portion is designed for insertion through the recessed, hollow socket and out through the aperture. The short, rod-shaped cylindrical head portion is designed to seat within the recessed, hollow socket. The novel orthopaedic hook member is adapted for limited angular movement within the recessed, hollow socket in a plane perpendicular to the axis of the central bore of the block-shaped member. This angular movement is about the axis of the short, rod-shaped cylindrical head portion, which axis is spaced apart from and parallel to the axis of the central bore. The "ball-headed" surgical screw is another removable anchor attachment for use with the invention. The recessed, hollow socket and the aperture pass the shank and threaded end of the screw while the hollow socket retains and seats the ball head of the screw in a "ball and socket" arrangement.
Accordingly, a principal object of the present invention is to provide an orthopaedic device capable of achieving improved mechanical alignment and coupling between a selected vertebra of the human spine and a longitudinally extending surgical rod.
Another object is to provide an orthopaedic device having an angularly adjustable anchor attachment member for providing improved alignment with and attachment to a selected vertebra of the spine.
Yet another object is to provide an improved orthopaedic hook member providing limited angular movement in a plane perpendicular to the axis of a longitudinally extending surgical rod to which the hook member is to be coupled.
Still another object is to provide an orthopaedic device, modular in design, adapted for receiving and supporting any one of a number of removable anchor attachment members of different shapes, openings and lengths.
An additional object is to provide an orthopaedic hook adapted for limited angular positioning about an axis spaced apart from and parallel to the axis of a surgical rod to which the orthopaedic hook is to be coupled.
A further object is to provide an orthopaedic device which, after attachment to a selected vertebra, is easier to align and to attach to an elongated surgical rod.
The above objects of and the brief introduction to the present invention will be more fully understood, and further objects and advantages will become more apparent, from a study of the following detailed description in connection with the drawing.